JJf.Vtf 


B.  P.  I.-4W.  Issued  October  3,  1908 


United  States  Department  of  A 

BUREAU  OF  PLANT  INDUSTRY— Circulai 
B.  T.  GALLOWAY,  Chief  of  Bureau 


THE  FERTILIZING  VALUE  OF  HAIR 
CONNECTICUT  TOBACCO  FIEI 

By  T.  R.  Robinson, 
Assistant  Physiologist,  Soil  Bacteriology  Investigai 


INTRODUCTION. 


In  connection  with  the  introduction  of  a  leguminous  cover  crop  on 
tobacco  lands  in  Connecticut  it  became  at  once  desirable  to  know  to 
what  extent  such  a  crop  would  lessen  the  need  for  fertilizers,  especially 
those  supplying  nitrogen.  Many  experiments,  mainly  based  on  analyses 
of  legumes,  might  lie  cited  to  show  the  amount  of  nitrogen  which 
legumes  furnish  to  a  succeeding  crop.  Their  very  disparity  serves  to 
indicate,  however,  that  the  results  may  be  largely  influenced  by  soil 
and  climatic  conditions,  so  that  for  any  one  locality  the  results  obtained 
elsewhere  might  prove  misleading. 

ADAPTABILITY  OF  HAIRY  VETCH  TO  TOBACCO  FIELDS. 

Mr.  A.  D.  Shamel,  of  the  Bureau  of  Plant  Industry,  published  in 
1905,  in  cooperation  with  the  Connecticut  Agricultural  Experiment 
Station,  the  preliminary  facts  in  regard  to  "a  new  and  valuable  cover 
crop  for  tobacco  fields,"  namely,  Russian  or  hairy  vetch  (  Vicia  villosa).1 
This  legume  was  found  to  be  resistant  to  cold,  heat,  and  drought; 
occupied  the  ground  during  the  fall,  winter,  and  spring;  decayed  rapidly 
when  turned  under;  and  enriched  the  soil  by  its  ability  to  "fix"  or 
utilize  atmospheric  nitrogen  when  properly  inoculated — that  is,  when 
the  bacteria  were  present  to  cause  the  formation  of  root  nodules.  Unless 
the  bacteria  were  artificially  supplied  it  was  found  that  the  desired 
inoculation  was  lacking  or  very  tardy  on  the  tobacco  lands  of  the  Con- 
necticut Valley. - 

1  See  Conn.  Agr.  Expt.  Sta.  Bui.  L49. 

2  "The  roots  of  plants  from  inoculated  seed  bore  main  tubercles,  some  aggre- 
gations  of  them  being  as  large  as  corn  kernels.  When  the  seed  was  not  inocu- 
lated the  roots  bore  few,  if  any,  nodule-  and  the  gro\vth  of  the  i>laiit>  was  much 
less  vigorous."     (Conn.  Agr.  Expt.  Sta.  Bui,  149,  p.  6.) 


2  FERTILIZING    VALUE    OF   HAIRY   VETCH. 

IMPORTANCE  OF  INOCULATING  HAIRY  VETCH. 

If  hairy  vetch  was  to  prove  at  all  valuable  as  a  fertilizer,  it  was  nec- 
essary to  get  the  crop  well  inoculated.  Plat  experiments  in  collabora- 
tion with  Mr.  Shamel  were  therefore  undertaken  in  the  autumn  of 
1906  at  Hockanum,  Conn.,  by  the  Office  of  Soil  Bacteriology  Inves- 
tigations to  determine,  if  possible,  the  value  of  hahy  vetch  as  a  fertili- 
zer on  the  soil  of  that  region.  Tobacco  following  uninoculated  vetch 
has  shown  but  little  advantage  over  that  following  a  rye  cover  crop,  but 
where  hairy  vetch  has  been  inoculated  and  an  abundance  of  root 
nodules  have  resulted  the  tobacco  following  has  been  greatly  benefited 
both  as  to  yield  and  as  to  quality.  When  one  compares  the  growth  of 
inoculated  and  uninoculated  vetch  this  will  be  easily  understood. 

The  yield  of  hairy  vetch  in  1907  at  Hockanum,  Conn.,  as  found 
from  sample  cuttings  on  1  square  rod  of  our  test  plats,  amounted  to  7 
tons  400  pounds  an  acre  (green  weight)  for  the  inoculated  vetch  and  2 
tons  240  pounds  an  acre  for  the  uninoculated  vetch.  Rye  on  this  land 
made  a  vigorous  growth,  yielding  at  the  rate  of  7  tons  720  pounds  an 
acre. 

To  determine  further  whether  the  difference  in  yield  in  this  test  cor 
be  due  to  any  difference  in  soil  nitrogen,  determinations  of  total  ni 
.    gen  in  samples  of  the  soil  were  made  by  the  Bureau  of  Chemistry, 
was  found  that  the  soil  where  vetch  was  growing  without  inoculatio 
contained  0.19  per  cent  of  total  nitrogen,  or  more  than  that  found  on 
either  the  plats  of  rye  (0.17  per  cent)  or  inoculated  vetch  (0.14  per 
cent).     Yet  with  this  greater  source  of  nitrogen  in  the  soil  the  vetch 
lacking  nodules  made  less  than  one-third   the  growth  attained  where 
the  plants  were  properly  inoculated.     It  may  be  said  that  in  one  case 
nodules  were  absolutely  lacking,  while  in  the  other  the  nodules  were 
so  abundant  that  when  the  vetch  was  plowed  under  the  upturned  soil 
was  dotted  white  with  the  glistening  nodules. 

POT  EXPERIMENTS  WITH  HAIRY  VETCH. 

To  check  under  controlled  conditions  the  results  obtained  in  the  tests 
at  Hockanum,  Conn.,  a  quantity  of  soil  from  the  uninoculated  plat  was 
shipped  to  Washington  and  some  experiments  were  undertaken  in  the 
greenhouse.  This  soil  was  placed  in  large  pots  (holding  about  30 
pounds  of  soil  each)  and  planted  with  seed  of  hairy  vetch,  ten  plants 
to  a  pot.  One-half  of  the  pots  were  sown  with  seed  treated  with  a  pure 
culture  of  the  vetch-nodule  organism,  the  remainder  being  untreated. 
The  pots  were  watered  throughout  with  water  sterilized  by  boiling. 
Despite  this  precaution  and  a  preliminary  sterilizing  of  the  pots  and 
seeds,  a  partial  inoculation  of  the  control  plants  took  place — probably 
due  to  insects  traveling  from  the  inoculated  pots.  This  chance  inocu- 
lation occurred,  however;  too  late  to  benefit  the  control  plants  as  much 


FERTILIZING    VALUE    OF    IIUKY    VETCH. 


as  those  inoculated  at  the  start,  and  the  difference  was  still  noticeable 
after  three  months' growth  (Decemher  11,  1907,  to  March  19,  190? 

Rye  was  grown  under  the  same  conditions   hut  did   not  make  a  very 
good  growth.      Plants  were   taken  "IT  for  weighing  when   flowers   b( 
to  appear,  and  samples  from  each  lot  weic  analyzed.    The  results  are 
shown  in  the  following  table: 

Table  I.— Results  of  greenhoust  tests  of  rye  and  inoculated  mid  uninoculated 

hairy  vetch. 


Two  p  ninis  twenty 

plants. 


weight 


Hairy  i 

Mnirv  vetch,  inoculated  plants 

Rye 


Gram*. 

It-  5 
215.5 

7-' 


Di  v  weight. 


Oram*. 


nitrogen 
fin  nisi 


/■.  i  i  nit. 

3.41 
8.49 


Oram  s. 


0.82 
1  18 
0.27 


It  will  be  seen  that  even  when  partial  inoculation  of  the  vetch  took 
place  the  highest  results  both  as  to  yield  and  percentage  of  nitrogen 
were  obtained  when  artificial  inoculation  was  practiced  and  that  both 

its  of  the  legume  w<  re  superior  to  rye  in  furnishing  nitrogen, 

wh  Vs  a  check  against  chance  inoculation,  a  few  small  pots  of  the  same  soil 

the  that  used  in  the  greenhouse  test  were  sterilized  by  autoclaving  for  1 

of    ur  at  140°  C.part  of  them  being  planted  with  inoculated  vetch  seed. 

The  pots  were  kept  in  a  glass  cage,  carefully  protected  against  insects 

or  dust  infection,  and  were  watered  with  sterile  distilled  water.     The 

checks  remained  free  of  nodules  throughout  the  experiment,  while  those 

inoculated  were  plentifully  supplied  with  nodules.     The  soils  were  so 

injured  by  the  heating  that  neither  set  of  plants  made  a  normal  growth, 

their  chief  difference  being  in  color.     The  check  plants  were  pale  green, 

while  the  inoculated  plants  were  healthy  in  color. 

NITROGEN  FURNISHED  BY  HAIRY  VETCH  TURNED  UNDER. 

If  the  percentages  shown  in  Table  I  are  taken  as  representing  the 
nitrogen  content  of  the  field-grown  vetch  previously  mentioned,  it  will 
be  seen  what  an  enormous  gain  was  effected  by  abundant  inoculation. 
Assuming  one-fifth  of  the  green  weight  to  represent  the  dry  weight  of 
the  vetch,  the  following  amounts  of  nitrogen  were  furnished  on  the 
cover-crop  plats  at  Eockanum,  Conn  : 

Table  II.  —  Comparison  of  nitrogen  in  cover  crops  of  rye  and  inoculated  an  I  unin 
oculattd  hairy  vetch  grown  at  Hockanum,  Conn. 


Plat. 


Green  weight, 
per  acre. 


Dry  weight, 

per  acre. 


Nitrogen. 


Hairy  vetch,  inoculated... 
Hairy  vetch,  uninoculated 
Rye 


1 

11,4(10 

1.240 

14,720 


Pounds. 

- 
848 


Pir  cent 

3.49 

H 

l.i,9 


Founds  per  arrt 
100.51 

49.75 


4  FERTILIZING   VALUE   OF   HA  TRY   VETCH, 

The  difference  in  the  quantities  of  nitrogen  furnished  by  the  two 
lots  of  field-grown  vetch  is  probably  even  greater  than  that  shown  here, 
owing  to  the  partial  inoculation  of  the  pot-grown  vetch  plants  from 
which  the  percentage  of  nitrogen  was  obtained.  It  is  not  to  be  con- 
cluded, however,  that  100.51  pounds  of  nitrogen  in  one  case  represents 
the  net  gain  from  growing  inoculated  vetch,  or  even  that  the  difference 
between  100.51  pounds  and  28.91  pounds  (71.6  pounds)  represents 
exactly  the  amount  of  nitrogen  abstracted  from  the  air  by  the  root- 
nodule  bacteria.  A  very  considerable  part  of  the  nitrogen  even  in  the 
case  of  an  inoculated  plant  is  derived  from  the  soil.  The  more  vigor- 
ous the  plant  and  more  wide  spreading  its  root  system,  the  greater  will 
be  its  ability  to  secure  nitrogen  from  the  soil. 

If,  however,  this  71.6  pounds  of  nitrogen  is  counted  as  clear  gain 
(that  is,  taken  from  the  store  of  atmospheric  nitrogen)  it  can  not  be 
assumed  that  this  becomes  at  once  available  for  the  succeeding  crop. 
There  is  reason  to  believe  that  the  greater  portion  of  it  becomes  avail- 
able under  favorable  conditions  within  a  comparatively  short  time,  but 
it  can  not  be  stated  as  proved,  for  instance,  that  this  amount  of  nitrogen 
turned  under  (71.6  pounds)  is  equivalent  to  the  application  of  475 
pounds  of  nitrate  of  soda  (15  per  cent  nitrogen). 

POT  EXPERIMENTS  WITH  TOBACCO. 

To  carry  the  pot  experiments  still  farther  the  soil  in  each  pot  was 
thoroughly  stirred  and  prepared  for  setting  out  tobacco  plants.  In  part 
of  the  series  the  vetch  or  rye  was  turned  under  and  in  part  removed 
entirely  from  the  pot.  The  pots  were  kept  moist  for  four  weeks,  tap 
water  being  used,  to  allow  for  the  decomposition  of  the  plants  turned 
under. 

Sodium  nitrate  was  chosen  as  a  carrier  of  nitrogen  to  compare  with 
that  furnished  by  the  plants  turned  under  and  was  supplied  at  the  rate 
of  200  pounds  to  the  acre  three  days  before  setting  out  the  tobacco  plants. 
To  get  the  maximum  effect  of  this  fertilizer  some  duplicate  pots  on 
which  no  cover  crop  had  been  grown  were  fertilized  at  the  rate  of  200 
and  500  pounds  of  sodium  nitrate  to  the  acre. 

Selected  tobacco  plants  from  Connecticut  seed,  apparently  of  equal 
size  and  vigor,  were  set  out  in  the  pots,  a  single  plant  to  a  pot.  The 
pots  were  watered  with  tap  water  from  this  time  to  the  completion  of 
the  experiments  (April  16  to  July  22,  1908).  The  tobacco  did  not  do 
especially  well  under  greenhouse  conditions,  but  all  plants  were  affected 
alike.  As  all  the  vetch  plants  turned  under  were  considerably  inocu- 
lated when  taken  up,  no  separate  account  was  kept  of  the  inoculated 
and  control  series.  The  fertilizer  used  was  200  pounds  of  sodium 
nitrate  to  the  acre.  The  results,  given  in  terms  of  the  green  weights  of 
the  plants  cut  off  at  the  surface  of  the  soil,  follow: 


FERTILIZING    VALUE   OF   HAIRY   VETCH 

Ounces  of 
Cover  crop  and  method  of  use.  Treatment  tobacco." 

Hairy  vetch  turned  under No  fertilizer 5.75 

Hairy  vetch  removed                      Fertilized 5.28 

Bairj  vetch  turned  under Fertilized  ....   ...    7.7"' 

Rye  turned  under          . No  fertilizer (.25 

Rye  removed Fertilized 5.25 

Rye  turned  under Fertilized 6 

■Average  of  four  pots. 

It  would  thus  appear  that  the  turning  under  o\  the  inoculated  hairy 
vetch  was  Blightly  superior  to  the  application  of  200  pounds  of  sodium 
nitrate  to  the  acre,  while  the  turning  under  of  rye  was  inferior  to  the 
application  of  the  fertilizer.  When  the  cover  crops  were  turned  undei 
and  fertilizer  added  the  vetch  again  Bhowed  greater  fertilizing  power 
than  rye.  In  pots  which  had  home  no  cover  crop  the  application  of 
nitrate  of  soda  at  the  rate  of  500  pounds  to  the  acre  was  no  more  effec- 
tive than  the  use  of  200  pounds  to  the  acre. 

CONCLUSIONS. 

In  presenting  this  report,  no  mention  has  been  made  of  the  influence 
on  the  soil  of  the  hairy  vetch  crop  aside  from  its  property  when  inocu- 
lated of  furnishing  nitrogen,  thus  allowing  a  considerable  reduction  in 
quantity  of  the  expensive  nitrogenous  fertilizer?.  As  a  preventive  of 
wind  and  water  erosion  the  matlike  growth  of  hairy  vetch  gives  it  great 
value;  as  a  source  of  humus  its  extensive  root  system  and  the  readily 
decomposable  nature  of  the  whole  plant  are  peculiar  advantages,  and  it 
seems  to  possess  in  addition,  on  land  successively  cropped  to  tobacco, 
a  green-manuring  value  considerably  above  its  purely  chemical  content 
and  the  physical  improvement  of  the  soil  resulting  from  its  use.  The 
full  nature  and  amount  of  these  benefits  will  require  more  extensive 
tests,  but  the  results  here  reported  are  presented  as  a  partial  guide  to 
those  interested  in  the  utilization  of  hairy  vetch  as  a  cover  and  fertiliz- 
ing crop. 

O 


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